1. Field of the Invention
The present invention relates to an electronic device, and particularly to an electronic device provided with means for preventing an undesirable effect or erroneous operation resulting from fluctuation of the voltage from a power source supplying the device with a driving voltage.
2. Description of the Prior Art
There have been known various power sources for supplying power to electronic devices, but the undesirable effect on the electronic devices due to fluctution of voltage is a serious problem, particularly in the case where a battery is employed as the power supply. As an example, a liquid crystal display (hereinafter referred to as an LCD) which is commonly used for an information display unit in a small electronic calculator is frequently driven by an alternating current, namely in such a way that the voltage across the electrodes of an LCD averaged in time is zero or is close thereto, in order to extend the lifetime of an LCD element.
However, in case an LCD is driven by a power source with a considerable fluctuation of voltage, such as a battery, a supply voltage outside of a certain tolerance range fails to provide normal operation of the drive circuit of the LCD or the logic unit or control unit for generating an indicator signal for the LCD, thus leading to a situation where the voltage applied to the LCD averaged in time is not equal or close to zero. In such a case, the lifetime of the LCD is significantly shortened. Further, fluctuation of the voltage causes erroneous calculation. In order to prevent the drawbacks mentioned above, it has been attempted in prior art electronic devices to supply the subject circuit with a power supply voltage through a voltage stabilizing circuit in order to reduce the effect of fluctuation of the voltage, or to provide a voltmeter for indicating the voltage of the power supply, thereby instructing the user to recharge or replace the battery contained in the electronic device when the indication of such voltmeter reaches a certain limit voltage.
However, the output characteristics of such a voltage stabilizing circuit change when the voltage supplied thereto is located outside the particular voltage control range, and become unsuited for driving the electronic device in a stable manner. Also, the users of such electronic devices often do not notice such a change in the output voltage of the power source.
Further, a voltmeter provided on the electronic device for indicating the output voltage of the power source requires constant attention by the users as to whether the voltage of the battery is located within a range allowing stable operation, and this becomes burdensome to the users.